Various curable and foamable phosphazene polymers have been disclosed in the prior art. For example, U.S. Pat. No. 3,856,713 describes the preparation of elastomeric poly(aryloxyphosphazene) copolymers. Because these copolymers are solid, fabrication of products therefrom, e.g., by foaming, requires high temperatures. Furthermore, these copolymers are crosslinked by conventional methods requiring high temperatures or use of radiation, such as peroxide curing and sulfur curing (vulcanization).
U.S. Pat. No. 4,107,146 discloses cured phosphazene polymers substituted with aryloxy groups and a group capable of a crosslinking chemical reaction (such as an alkenyl substituted aryloxy) and the process for curing. These polymers are solid at room temperature and are crosslinked at elevated temperatures with conventional sulfur curing agents such as sulfur monochloride. The solid polymers must be heated to between 200.degree. F. and 350.degree. F. in order to be foamed.
U.S. Pat. No. 4,116,785 discloses phosphazene polymers substituted with alkoxy and aryloxy groups and with from 0.1 to 5 percent of the total substituents having olefinic unsaturation. These polymers are solid at room temperature. They are cured by conventional curing agents and require heating to about 300.degree. F. in order to be cured.
U.S. Pat. No. 3,676,311 discloses burn-resistant polymers prepared by photocuring a mixture of polythiol and a phosphonitrilic polymer containing at least two reactive unsaturated carbon-to-carbon groups. Solid and liquid cross-linkable polymers are produced and used in this manner. Some of them are cyclic polymers; others are linear. In preparing these polymers all or part of the halide atoms of a phosphonitrilic halide, preferably in cyclic form, are replaced by unsaturated groups, such as allyloxy and the like.
When preparing foams or crosslinked products it is desirable that the crosslinkable prepolymer be in liquid form at ambient temperatures as this facilitates handling and use.